1. Field of the Invention
The present invention relates to a pattern measurement apparatus and a pattern measurement method.
2. Related Background Art
The manufacture of a semiconductor device requires not only manufacturing steps such as a lithographic step, a film formation step and an etching step but also a step of measuring a micropattern created by the above-mentioned steps to improve yield. For a pattern measurement, a CD measurement using a critical dimension scanning electron microscope (CDSEM) has heretofore been performed.
Recently, in order to meet the demands for the increase of performance and function of a device, the size of a pattern has been increasingly smaller, and the two-dimensional and three-dimensional shapes of the pattern have also been increasingly complex as typified by a double patterning technique. In order to evaluate the pattern having such complex shapes, it is necessary to measure the sectional shape of the pattern in contrast with the conventional CD measurement which only measures the CD of a particular part of the pattern section.
Conventionally, a method based on a destructive measurement by, for example, a sectional SEM or a transmission electron microscope (TEM) has been used for the measurement of pattern sections. On the other hand, due to increasing demands for the measurement of pattern sections in a nondestructive manner, scatterometry using light has been recently becoming more popular. The technique of the scatterometry is as follows: Light is applied to a measurement target pattern, and the spectral waveform of the reflected light is used to estimate a corresponding pattern sectional shape and an index of refraction by referring to a waveform library which depends on the pattern sectional shape previously constructed by a numerical calculation (refer to Japanese Patent Laid-open Pub. No. 2005-142535).
The scatterometry is advantageous not only in that it is a nondestructive measurement but also in that it is capable of measuring, for example, the height and sidewall angle as well as CD of a pattern. On the other hand, the disadvantage of the scatterometry is that it requires previous construction of the waveform library, which demands a great amount of work. In particular, in order to create a model which approximates the pattern sectional shape by, for example, a trapezoid, it is necessary to previously know the change of the pattern sectional shape corresponding to process variations. To this end, know-how is required to perform modeling of the section of the pattern by watching a photograph thereof.
As described above, to obtain a highly accurate measurement result, a great amount of cost (labor and time for a skilled engineer) is needed to create a good waveform library, which has been a heavy burden. Another disadvantage is measurement robustness which prevents, even if a measurement is thus made with much cost, a correct measurement value from being calculated for an unexpected pattern sectional shape that is not contained in the waveform library due to, for example, to process variations.